This paper provides a process-oriented perspective on the combined effects of ozone (O-3), climate change and/or nitrogen (N) on vegetation. Whereas increasing CO2 in controlled environments or opentop chambers often ameliorates effects of O-3 on leaf physiology, growth and C allocation, this is less likely in the field. Combined responses to elevated temperature and O-3 have rarely been studied even though some critical growth stages such as seed initiation are sensitive to both. Under O-3 exposure, many species have smaller roots, thereby enhancing drought sensitivity. Of the 68 species assessed for stomatal responses to ozone, 22.5% were unaffected, 33.5% had sluggish or increased opening and 44% stomatal closure. The beneficial effect of N on root development was lost at higher O-3 treatments whilst the effects of increasing O-3 on root biomass became more pronounced as N increased. Both responses to gradual changes in pollutants and climate and those under extreme weather events require further study. (C) 2015 Elsevier Ltd. All rights reserved.